Ferroelectric materials possess a net permanent dipole moment μ. If the dipoles point in the same direction a spontaneous polarization, P, appears and the solid is called ferroelectric. The temperature T derivative of the polarization P, dP/dT is the pyroelectric coefficient. It is the pyroelectric coefficient, inherent to all ferroelectrics, that leads to an electrical charge or current at the surface of a solid that is a limitation of ferroelectric solids in sensor configurations. Today, sensors for detecting electromagnetic radiation are part of the mental furniture of researchers. They are typically tuned or constructed for sensing electromagnetic radiation within a specific wavelength, λ, of the electromagnetic spectrum. For example, they may be tuned for x-ray, (10−6 to 10−8 cm), gamma ray, (10−8 to 10−1 cm), infrared, (10−2 to 10−4 cm). Devices using such technologies can be as simple as a household motion detector or memory devices to sophisticated astrophysics instruments and sophisticated instruments used in physics experiments. Infrared sensors are of particular interest and are used in high speed FTIR (Fourier Transform Infrared Spectroscopy), night vision instruments, particular those used by soldiers, astronomical telescopes and the like. Several types of sensors for detecting infrared radiation are known in the art. Some of these are discussed in U.S. Pat. No. 5,406,081. Of particular interest in this invention is the control of the pyroelectric current. In order to use the pyroelectric effect of the various ferroelectric materials, one needs to remove the surface charge on the sensor element. One way of doing this has been to enclose the sensor in a hermetically sealed area containing argon or neon gas (see U.S. Pat. No. 5,406,081). A window for transmitting the infrared radiation from the environment to the sensor is required and can be made from a material such as KBr or Teflon.
Surface charge, originating from dP/dT may also be reduced by the application of a layer of conductive material, e.g., polymer or metal, to the ferroelectric material. However, such requirements are expensive to implement and often adversely affect the performance.
Thus, there is a need for an improved sensor and method for assessing ferroelectric materials for functionality and critical parameters.